A new low-dose oral contraceptive pill reduces symptoms of premenstrual syndrome, including a severe form called premenstrual dysphoric disorder, researchers report.

"Oral contraceptives are commonly used for premenstrual conditions, usually milder syndromes, but the empirical evidence supporting their use has been lacking," Dr. Kimberley A. Yonkers of Yale University School of Medicine, New Haven , Connecticut , told Reuters Health. "This is the first study to show that an oral contraceptive is better than placebo for any premenstrual syndrome, including premenstrual dysphoric disorder."

The agent contains "a low dose of ethinyl estradiol -- 20 micrograms -- and a newer progestin, drospirenone, that is an analog of the diuretic agent, spironolactone," she explained.

To investigate its effects, Yonkers and colleagues randomly assigned 450 women with symptoms of premenstrual dysphoric disorder to receive the oral contraceptive or placebo. The active formulation was administered for 24 days followed by 4 days of inactive pills.

"Response, defined as a 50 percent decrease in daily symptoms scores, occurred in 48 percent of the active-treatment group and 36 percent of the placebo group," the team reports in the medical journal Obstetrics and Gynecology.